The invention relates to a universal and generic system of environmental stress screening (ESS) of electronic devices such as printed wiring board assemblies. The devices are placed in a chamber and are temperature cycled at high and low limits. The temperature cycling causes stress in the electronic devices and serves to identify weak and defective mechanical joints, such as solder joints, in the components prior to being shipped to the customer. It is essential to note that environmental stress screening (ESS) is not a test for electronic devices but a stressing of electronic devices to weed out weak and defective components. Testing of the devices must take place both before and after environmental stress screening (ESS) to identify those devices that were forced to failure.
In prior chambers, stress screening was performed in chambers that limited quantity or transition rates between temperature extremes. The need for greater reliability and quality has increased and it has become common for stress screening to be performed in a more efficient and cost effective manner. As a result a chamber for production oriented environmental stress screening (ESS) that can stress devices as part of production line processes is required. Large chambers have been developed that are not adaptable or economically feasible for small to medium volume manufacturers, such as the Environmental Stress Screening Apparatus of Keel, et al, U.S. Pat. No. 4,812,750, for high production manufacturers. Small specialized chambers also have been designed to stress screen semiconductor devices, such as the Thermal Stress Screening System of Lesley, et al, U.S. Pat. No. 4,854,726. A need for small, highly efficient, affordable, and convertible ESS chambers exists for those manufacturers whose volume of business does not justify large capital outlay but whose market requires high quality goods.
This invention provides a means for the small to medium volume manufacturer to stress all electronic devices at a justifable cost and allows for relatively simple reconfiguration to accommodate a variety of devices.